In nanotechnology, one of the key techniques is to achieve fine positioning with a sub-micrometer resolution. For example, in scanning probe microscopy, the probe has to be brought close to a sample from a few mm apart to within a distance of only a few nanometers. There are many other applications wherein fine positioning and motion of articles are required.
An early type of a piezoelectric inchworm motor was disclosed by William G. May, Jr., in his U.S. Pat. No. 3,902,084, “Piezoelectric electromechanical translation apparatus” (assigned to Burleigh Instruments, Inc.). Later, H. Atsushi et al. disclosed a modification to May's invention in their U.S. Pat. No. 4,570,096, “Electromechanical translation device comprising an electrostrictive driver of a stacked ceramic capacitor type” (assigned to NEC Corporation.). They are used for micropositioning in scanning tunneling microscopes and atomic force microscopes.
Another type of an inchworm linear motor, based on the same operation mechanism as the Burleigh inchworm but with a very different mechanical design, also applied to scanning tunneling microscopes, was disclosed by one of the inventors of this invention in his Ph.D thesis: I. S. Hwang, “Tunneling microscopy of dynamical processes on the PB/GE(111) surface, Harvard University, Division of Applied Sciences, 1993, Chapter 2.
The device included a cylindrical movable shaft and a stage that contains an expansible/contractible device for driving the movable shaft and two clamps. The stage, the expansible/contractible device, and the two clamps were all machined from a single MACOR piece. The motion of the expansible/contractible device and the clamping/unclamping of the two clamps were separately controlled by three similar bimorph structures. Each bimorph structure was made by gluing a cut cylindrical piezoelectric tube section to a hole with a thin wall in the MACOR piece. This structure is compact and rigid, thus it exhibits very good mechanical stability against mechanical vibrations. However, the outer surface of the movable shaft and the surfaces of the two clamps that make contact with the shaft have to be machined with precision and accuracy better than 10 micrometers; otherwise the clamping and unclamping motions cannot be actuated properly. Another problem is that the shaft may rotate along its axis during the translational motion.